Broadly speaking, this invention relates to periodic piezoelectric structures. More particularly, in a preferred embodiment, this invention relates to periodic, piezoelectric structures which are fabricated from high resistivity, semiconducting crystals, such as those in cubic class 43 m.
The frequency range of 100 to 300 GHz is of great interest to both military and civil authorities. Among the possible uses for this frequency band are fixed and mobile radar systems, terrestrial and satellite communications systems, etc. Unfortunately, heretofore, no satisfactory detector or monochrometer has been available for use of these high frequencies, which factor has greatly retarded the development of millimeter wave systems of this type.
While the piezoelectric properties of high-resistivity semi-conductor material, such as GaAs, have been widely reported in the literature, we have discovered that these properties may be used to fabricate a periodic, piezoelectric structure that can be used to detect and transmit millimeter waves in the aforesaid 100-300 GHz range. Indeed, it is anticipated that the instant invention will generate an entirely new class of piezoelectric devices including detectors, filters, monochrometers, and signal processing devices.
It is pointed out that periodic structures have been fabricated which make use of variation in electrical properties from layer to layer.
In the present invention, however, the alternating layers are not electrically active, no donors or acceptors of electrons present, but are piezoelectrically active, highly insulating dielectrics with permanent electric dipoles being coupled to mechanical stress fields with acoustic mismatch, or piezoelectrically inactive insulators with acoustic mismatch.